Standardization of the Dmax Method for Calculating the Second Lactate Threshold

in International Journal of Sports Physiology and Performance
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Purpose:

The purpose of this study was to test the reliability and validity of 2 standardized methods for calculating speed at the second lactate-threshold point (LT2) based on the preexisting Dmax (LTD) and modified Dmax (LTMOD) procedures.

Methods:

13 trained male road runners and triathletes completed 2 incremental laboratory running tests to determine LT2, followed by separate time trials (5, 10, 15 km) on an outdoor running track. Two new methods were proposed for calculating the speed at LT2: (1) the single standardized lactate threshold (LTSDs) and (2) the paired standardized lactate threshold (LTSDp) for quantifying changes over time.

Results:

The LTSDs and LTSDp methods had high relative (ICC ≥ .98) and absolute (CV ≤ 1.9%) reliability in identifying the speed at LT2. The speed at LT2 according to the LTSDs and LTSDp methods had a strong correlation and was not different to the performance speed during the 10- and 15-km time trials (≤2.3%; ρc > 0.8; P > .05). The following natural logbased formula was created to estimate the percentage of LT2 speed (using the LTSDs method) that could be sustained for events ~15–75 min: y = –7.256(ln x) + 157.64, where y = %LT2 speed, x = time-trial performance (s), and ln = natural log.

Conclusions:

The standardized methods are reliable for determining LT2. The LTSDs and LTSDp methods for calculating the speed at LT2 from a near-maximal incremental test calculated speeds similar to those exhibited in 10- and 15-km running time trials. A prediction equation for estimating the percentage of LT2 that can be sustained for events of ~15–75 min was generated.

Chalmers, Eston, and Norton are with the Alliance for Research in Exercise, Nutrition, and Activity, and Esterman, the School of Nursing and Midwifery, University of South Australia, Adelaide, Australia.

Address author correspondence to Samuel Chalmers at samuel.chalmers@mymail.unisa.edu.au.